Synthesis, Characterization, and in vitro Testing of a Bacteria-Targeted MR Contrast Agent.

A bacteria-targeted MR contrast agent, Zn-1, consisting of two Zn-dipicolylamine (Zn-dpa) groups conjugated to a GdIII chelate has been synthesized and characterized. In vitro studies with S. aureus and E. coli show that Zn-1 exhibits a significant improvement in bacteria labeling efficiency vs. control. Studies with a structural analogue, Zn-2, indicate that removal of one Zn-dpa moiety dramatically reduces the agent's affinity for bacteria. The ability of Zn-1 to significantly reduce the T1 of labeled vs. unlabeled bacteria, resulting in enhanced MR image contrast, demonstrates its potential for visualizing bacterial infections in vivo.